Induction of a transient acidosis in the rumen simulation technique

Feeding high concentrate diets to cattle results in an enhanced production of short‐chain fatty acids by the micro‐organisms in the rumen. Excessive fermentation might result in subclinical or clinical rumen acidosis, characterized by low pH, alterations in the microbial community and lactate production. Here, we provide an in vitro model of a severe rumen acidosis. A transient acidosis was induced in the rumen simulation technique by lowering bicarbonate, dihydrogen phosphate and hydrogen phosphate concentrations in the artificial saliva while providing a concentrate‐to‐forage ratio of 70:30. The experiment consisted of an equilibration period of 7 days, a first control period of 5 days, the acidosis period of 5 days and a second control period of 5 days. During acidosis induction, pH decreased stepwise until it ranged below 5.0 at the last day of acidosis (day 17). This was accompanied by an increase in lactate production reaching 11.3 mm at day 17. The daily production of acetate, propionate and butyrate was reduced at the end of the acidosis period. Gas production (methane and carbon dioxide) and NH₃‐N concentration reached a minimum 2 days after terminating the acidosis challenge. While the initial pH was already restored 1 day after acidosis, alterations in the mentioned fermentation parameters lasted longer. However, by the end of the experiment, all parameters had recovered. An acidosis‐induced alteration in the microbial community of bacteria and archaea was revealed by single‐strand conformation polymorphism. For bacteria, the pre‐acidotic community could be re‐established within 5 days, however, not for archaea. This study provides an in vitro model for a transient rumen acidosis including biochemical and microbial changes, which might be used for testing feeding strategies or feed additives influencing rumen acidosis.     

In situ starch and crude protein degradation in the rumen and in vitro gas production kinetics of wheat genotypes

The objective of this study was to determine the variation of in situ ruminal degradation characteristics of dry matter (DM), crude protein (CP) and starch (ST), and to determine the effective degradation (ED) of wheat genotypes. Further, multivariate associations of these in situ values with their corresponding in vitro gas production (GP) kinetics and laboratory measurements were evaluated using correlation and multiple linear regression analyses. Grains of 20 genotypes of wheat were characterized by proximate constituents, amino acid (AA) composition and physical characteristics. Ruminal degradation kinetics were determined by in situ degradation of DM, CP and ST, and subsequent evaluation of in vitro GP relative to time courses. In situ and GP measurements were fitted to an exponential equation, and ED was calculated using passage rates in the rumen of 5%/h (ED5) and 8%/h (ED8). To predict ED8 of CP (EDCP8) and ST (EDST8), correlations were evaluated and stepwise multiple linear regression analyses were applied. Estimated degradation parameters varied considerably between wheat genotypes irrespective of the nutrient tested. Variance in a, b and c was not reflected in the variation of the ED, due to high degradation rates (c). The assumed passage rate also impacted estimation of the ED minimally. Estimated GP parameters varied only slightly among wheat genotypes. Nevertheless, regression models explained up to 80 and 99% of the variance in EDCP8 and EDST8, respectively, and associations between EDST8 and EDCP8 and chemical and physical characteristics of grains were detected. As ST is the primary nutrient in wheat grains and can comprise substantial portions of dairy rations, the total amount of ST as well as its ED in the rumen should be taken into account when wheat is incorporated into dairy rations. Conversely, variance in wheat grain CP degradation was very low and can largely be neglected in practical ration formulation for ruminants.     

Effect of donor animals and their diet on in vitro nutrient degradation and microbial protein synthesis using grass and corn silages

Two nonlactating cows and two wether sheep, all fitted with a permanent cannula into the rumen, were fed either hay plus concentrate, grass silage or corn silage to study the effect of the donor animal and its diet on in vitro fermentation and microbial protein synthesis. Rumen inoculum was obtained before the morning feeding. Grass silage or corn silage was incubated in a semi‐continuous rumen simulation system for 14 days. Four replicated vessels were used per treatment. Degradation of crude nutrients and detergent fibre fractions as well as microbial protein synthesis and the production of volatile fatty acids were studied. Additionally, total gas and methane production was measured with a standard in vitro gas test. Gas production and methane concentration was higher when the inoculum used was from sheep than that from cows. The donor animal also affected the degradation of organic matter and ether extract as well as the amount of propionate and butyrate, and the acetate‐to‐propionate ratio. The effect of the diet fed to the donor animal on fermentation was much greater than the effect of the donor animal itself. Feeding hay plus concentrate resulted in higher gas production and degradation of acid detergent fibre, but in lower degradation of ether extract and reduced microbial protein synthesis. Additionally, the pattern of volatile fatty acids changed significantly when the diet of the donor animals was hay plus concentrate or one of the silages. These results show that in vitro fermentation and microbial protein synthesis is different when based on inoculum from either cattle or sheep. The diet fed to the donor animal is more important than the animal species and is probably mediated by an adjusted microbial activity. With regard to standardized feed evaluations, these results further support the need to harmonize in vitro approaches used in different laboratories.     

In vitro fermentation of feed ingredients by fresh or frozen pig fecal inocula

In vitro techniques can offer a rapid, repeatable and cost‐effective alternative to in vivo experiments. We investigated the gas production (GP) of nine different feeds commonly used in Italian and Maltese pig farms in order to assess the use of the Ankom system in this species and to compare the in vitro microbial activity fresh or frozen inocula derived from piglet feces. Proximate and polyphenolic analyses were determined for all substrates. Fermentation profiles were measured according to the cumulative GP technique. Analysis of GP values revealed significant differences in the fermentation patterns mainly due to substrate and inoculum effects. Fermentation parameters varied significantly according to the substrate ingredients. The frozen inoculum generally led to more total GP than for fresh, with the exception of hard wheat bran pellets (HWBP), pelleted pulp and mature carob. Conversely the fresh fecal inoculum had an earlier maximum time to reach maximum GP than the frozen, showing a higher maximum rate of GP in all substrates excepting for HWBP. A significant difference in frozen and fresh inocula was found for the complete formulation. Further studies are required to confirm the variation between fresh and frozen fecal inocula to a wider range of feed, including those that could have negative biological effects.     

Effects of different forms and origins of oilseeds on dynamics of ruminal biohydrogenation of long‐chain fatty acids in vitro

Dietary unsaturated fatty acids (FA) are intensively hydrogenated in the rumen, resulting in reduced amount of poly‐unsaturated fatty acids (PUFA) and accumulation of several biohydrogenation (BH) products. In this study, BH of PUFA originating from different oilseeds (linseed, soya beans, sunflower seed and rapeseed) present in crushed oilseeds or their free oils were assessed in vitro. The assay substrates were incubated in buffered rumen fluid for 0, 6, 12 and 24 h. After incubation, the FA pattern of the incubated samples was analysed using gas chromatography. Biohydrogenation is defined as disappearance of double bonds (DB) calculated from the contents of unsaturated FA. After 24‐h incubation, the DB contents of all oilseeds were reduced (p < 0.001) by 40–60%. The reduction was higher (p < 0.001) for the crushed form compared with the oil form. In addition, linseed and sunflower seed known as oilseeds with high contents of linolenic acid C18:3 c9,12,15 (LNA) and linoleic acid C18:2 c9,12 (LA), respectively, showed a higher (p < 0.001) accumulation of the BH intermediates conjugated linoleic acid (CLA, isomer C18:2 c9t11) and vaccenic acid (C18:1 t11) for the crushed form, when compared with the oil. These results suggest an inherent effect of the physical form of the assay oilseeds on in vitro BH. Changes in FA pattern during BH in vitro can be attributed to both source and physical form of the assay oilseeds. However, further investigations are warranted to ensure whether the observed in vitro effects on ruminal BH can be confirmed in vivo.     

Impact of variation in structure of condensed tannins from sainfoin (Onobrychis viciifolia) on in vitro ruminal methane production and fermentation characteristics

Our study investigated the effects of condensed tannins (CT) on rumen in vitro methane (CH₄) production and fermentation characteristics by incubating lucerne in buffered rumen fluid in combination with different CT extracts at 0 (control), 40, 80 and 120 g CT/kg of substrate DM. Condensed tannins were extracted from four sainfoin accessions: Rees ‘A’, CPI63763, Cotswold Common and CPI63767. Gas production (GP) was measured using a fully automated GP apparatus with CH₄ measured at distinct time points. Condensed tannins differed substantially in terms of polymer size and varied from 13 (Rees ‘A’) to 73 (CPI63767) mean degree of polymerization, but had relatively similar characteristics in terms of CT content, procyanidin: prodelphinidin (PC: PD) and cis:trans ratios. Compared to control, addition of CT from CPI63767 and CPI63763 at 80 and 120 g CT/kg of substrate DM reduced CH₄ by 43% and 65%, and by 23% and 57%, respectively, after 24‐h incubation. Similarly, CT from Rees ‘A’ and Cotswold Common reduced CH₄ by 26% and 46%, and by 28% and 46% respectively. Addition of increasing level of CT linearly reduced the maximum rates of GP and CH₄ production, and the estimated in vitro organic matter digestibility. There was a negative linear and quadratic (p < 0.01) relation between CT concentration and total volatile fatty acid (VFA) production. Inclusion of 80 and 120 g CT/kg of substrate DM reduced (p < 0.001) branched‐chain VFA production and acetate: propionate ratio and was lowest for CPI63767. A decrease in proteolytic activity as indirectly shown by a change in VFA composition favouring a shift towards propionate and reduction in branched‐chain VFA production varied with type of CT and was highest for CPI63767. In conclusion, these results suggest that tannin polymer size is an important factor affecting in vitro CH₄ production which may be linked to the CT interaction with dietary substrate or microbial cells.     

Contribution of different rumen microbial groups to gas,short‐chain fatty acid and ammonium production from different diets—an approach in an in vitro fermentation system

In this study, the relative contribution of different microbial groups to ruminal metabolism was investigated for different diets. The rumen microbial cultures included whole rumen fluid, fungi + protozoa, bacteria + protozoa, protozoa and bacteria + fungi and were established by physical and chemical methods. Gas production, short‐chain fatty acid (SCFA) and ammonium production were measured at 24 hr in in vitro incubations using the Hohenheim gas test (HGT) procedure. Seven donor animal diets with different concentrate‐to‐roughage ratios (C:R: 10:90, 30:70, 50:50, 70:30, 70:30BC (BC = NaHCO₃), 90:10 and 90:10BC) and five HGT diets (C:R: 10:90, 30:70, 50:50, 70:30 and 90:10) were formulated. Incubations in the HGT were always based on inoculum from sheep diets with the respective C:R ratio. Gas and ammonium production increased (p < 0.001) as a result of a gradual increase in concentrate proportion of the diets. In general, SCFA production followed the same trend. Whole rumen fluid and bacteria + fungi produced approximately 50% higher gas volume than protozoa and fungi + protozoa fractions, whereas gas production with bacteria + protozoa was at an intermediate level. Coculture of protozoa either with bacteria or with fungi produced more ammonium. Populations without bacteria were characterized by a particularly high acetate/propionate ratio. Although an interaction between microbial group and diet was observed for several variables, no clear direction could be established. Manipulating rumen fluid by selectively suppressing specific rumen microbial groups may be a helpful tool in elucidating their role in nutrient degradation and turnover in vitro.     

Ruminal phytate degradation of maize grain and rapeseed meal in vitro and as affected by phytate content in donor animal diets and inorganic phosphorus in the buffer

The ruminal disappearance of phytate phosphorus (InsP₆‐P) from maize grain and rapeseed meal (RSM) was determined in two in vitro studies. In experiment 1, two diets differing in phosphorus (P) and InsP₆‐P concentration were fed to the donor animals of rumen fluid (diet HP: 0.49% P in dry matter, diet LP: 0.29% P). Maize grain and RSM were incubated in a rumen fluid/saliva mixture for 3, 6, 12 and 24 h. In experiment 2, a diet similar to diet HP was fed, and the rumen fluid was mixed with artificial saliva containing 120 mg inorganic P/l (Pi) or no inorganic P (P0). Maize grain and RSM were incubated with either buffer for 3, 6, 12 and 24 h. Total P (tP) and InsP₆ concentration were analysed in the fermenter fluids and feed residues. The disappearance of InsP₆‐P from maize was completed after 12 h of incubation in both experiments. From RSM, 93% (diet LP) and 99% (diet HP) of the InsP₆‐P in experiment 1 and 80% (Pi) and 89% (P0) in experiment 2 had disappeared after 24 h of incubation. InsP₆‐P disappearance was higher when diet HP was fed (maize: 3 and 6 h; RSM: 6 and 24 h of incubation) and when rumen fluid was mixed with buffer P0 (maize: 6 h; RSM: 12 and 24 h of incubation). InsP₆‐P concentration in the fermenter fluids was higher for maize, but no accumulation of InsP₆‐P occurred, indicating a prompt degradation of soluble InsP₆. These results confirmed the capability of rumen micro‐organisms to efficiently degrade InsP₆. However, differences between the feedstuffs and diet composition as well as the presence of inorganic P in the in vitro system influenced the degradation process. Further studies are required to understand how these factors affect InsP₆ degradation and their respective relevance in vivo.     

Effects of a blend of garlic oil,nitrate and fumarate on in vitro ruminal fermentation and microbial population

Although garlic oil and nitrate can effectively suppress ruminal methane (CH₄) production in vitro, the application of these compounds is associated with suppressed total volatile fatty acid (VFA) concentration. On the other hand, the effectiveness of fumarate as a ruminal CH₄ mitigating agent is variable but its application increases total VFA concentration. We therefore hypothesized that the different characteristics of the compounds can compensate for the shortcomings of the other. The objective of this study was to develop an optimal blend of garlic oil, nitrate and fumarate that can suppress in vitro ruminal CH₄ without affecting total VFA concentration. Three ruminal in vitro fermentation experiments were carried out. The first one, a one factor at a time experiment was employed to investigate the effective concentration of each of the compounds on CH₄ and VFA production by ruminal bacteria. We then applied the fractional factorial design and response surface methodology in the second experiment to determine optimal concentrations of the compounds in the blend. The optimal blending of garlic oil, fumarate and nitrate was determined to be 50 mg/l, 15 mm and 20 mm , respectively. This simulated optimal blend was verified in a 48 h in vitro batch fermentation experiment. The blend achieved the intended goal of suppressing CH₄ whilst maintaining total VFA concentration. The blend and nitrate suppressed archaea populations (p < 0.001) but did not affect the total microbial population (p = 0.945). The observed results could be explained by additive effects of the agents making up the blend. Supplementing a high concentrate diet with the blend can significantly decrease ruminal CH₄ and maintain total VFAin vitro. These findings however, need to be verified in vivo using the optimized ratio of combining the three methane inhibitors as a guide.     

体外产气法评定植酸酶对稻糠、玉米麸和麦麸瘤胃发酵特性的影响

采用体外瘤胃发酵试验结合动态产气实时记录技术,分析了添加植酸酶对瘤胃微生物降解和利用糠麸饲料的功效。试验采集3头健康泌乳期荷斯坦奶牛瘤胃液,以稻糠、玉米麸和麦麸为底物,测定对照组和加酶组(5 U/g植酸酶)发酵72 h的累积产气量、发酵动力学参数和和瘤胃发酵特性指标。结果表明,添加5 U/g植酸酶并不能显著影响稻糠、玉米麸和麦麸的体外干物质消化率、培养液中氨态氮浓度以及发酵的产气量(72 h累积产气量和理论最大产气量)(P>0.050 0),但却能显著降低发酵的产气速率及达到最大产气量1/2时的产气速率(P<0.050 0),显著提高培养液总挥发性脂肪酸浓度(P<0.050 0),总挥发性脂肪酸浓度增幅由高至低依次为麦麸(4.2%)、稻糠(3.3%)和玉米麸(1.7%),除可显著提高异丁酸含量(P<0.050 0)外,对乙酸、丙酸、丁酸等主要挥发性脂肪酸的含量的影响不显著(P>0.050 0)。总之,稻糠、玉米麸和麦麸间体外瘤胃发酵特性存在差异,添加植酸酶可在一定程度上促进瘤胃微生物发酵释放出更多的挥发性脂肪酸,提高瘤胃微生物对饲料中能量物质的发酵利用效率。     

Rumen fermentation and degradability in buffalo and cattle using the in vitro gas production technique

An in vitro trial was conducted to investigate the effect of different inoculum sources (buffalo vs. cattle) on rumen fermentation and degradability. Incubations were carried out using rumen fluid obtained from buffalo or cattle fed the same diet [60% grass hay and 40% concentrate; 18 kg dry matter (DM)/day]. The fermentation kinetics of eight feeds commonly used in ruminant nutrition (alfalfa hay, barley meal, beet pulp, corn meal and silage, ryegrass hay and silage and soya bean meal s.e.) were studied with the in vitro gas production technique and rumen fermentation parameters (substrate disappearance, pH and volatile fatty acids production) were determined after 120 h of incubation. The linear relationship indicates that the microbial metabolic pathways of the two inocula for all the substrates were qualitatively similar, albeit often quantitatively different. In this in vitro study, a significant influence of rumen inoculum (buffalo vs. cow) on fermentation and degradability of the examined substrates was found. The differences in buffalo and cattle rumen fermentation can be explained with a different microbial activity of the two ruminant species, because of different amount of microbial population or microbial population constituted by different species of bacteria and protozoa.     

接种不同的瘤胃液与缓冲液比例对短期人工瘤胃发酵产气量及pH值的影响

应用短期人工瘤胃发酵技术,通过接种不同数量的瘤胃液,确定瘤胃液数量(微生物数量)对人工瘤胃发酵产气量及pH值的影响。试验分为10个处理,即缓冲液与瘤胃液体积比分别为11∶、21∶、31∶、41∶、51∶、61∶、71∶、81∶、91∶和101∶。每个处理设置2个重复,同时每个处理设置2个空白。将样品发酵48h,分别在2、4、8、12、24、48h6个时间点记录注射器活塞的位置,并在发酵结束时测定发酵液的pH值。结果表明:不同处理组2h和4h的产气量与瘤胃液比例极相关(P<0.01),8h和12h的产气量与瘤胃液比例显著相关(P<0.05),24h以后(包括24h)的产气量与瘤胃液比例不相关(P>0.05)。瘤胃液比例对人工瘤胃发酵的pH值没有影响。     

In vitro fermentation characteristics of different carbohydrate sources in two dog breeds (German shepherd and Neapolitan mastiff)

Few studies have been published on the normal intestinal biota of canines unlike the wealth of information regarding livestock animal species. The in vitro gas production technique (IVGPT) including measurements of accumulating gas during fermentation and end‐product determinations allows obtaining a complete picture of microbial activity kinetics. The aim of this study was to study the in vitro fermentation characteristics of different carbohydrate sources using inocula from two dog breeds (German Shepherd and Neapolitan mastiff). Faeces sampled from rectum of two GS and NM adult dogs, fed the same dry food, were used as inocula. The samples, diluted and filtered, were incubated at 39 °C under anaerobic condition with nine substrates different for carbohydrate composition (rice, corn, potato, spelt, pure cellulose, beet pulp, wheat bran, inulin and fructo‐oligosaccharide). Gas production was recorded 17 times using a manual pressure transducer. After 48 h, the fermentation was stopped and fermenting liquor was analysed for pH and volatile fatty acids (VFA). Organic matter digestibility (OMD) was calculated as difference after burning the residuals. OMD, gas production and end‐products were significantly correlated with chemical composition of substrates, in particular carbohydrate fractions (total dietary fibre and starch), confirming the effectiveness of the IVGPT in evaluating dog feeds. Concerning the comparison between breeds significant differences (p < 0.01) were found for OMD, gas production, fermentation kinetic parameters and end‐products, suggesting a different pathway of fermentation and consequently, a different anaerobic population.     

A model to assess the use of caecal and faecal inocula to study fermentability of nutrients in rabbit

An in vitro gas production trial was conducted using 10 Hyla rabbits to evaluate the use of caecal and faecal inocula in fermentability studies. Caecal content (CI) and hard faeces (FI) were used as inocula. Six legume and six cereal concentrates were used as substrates. Gas production was recorded 19 times at 2–24 h intervals throughout fermentation (120 h). The fermentation characteristics (degraded organic matter, OMd; potential gas production, A; volatile fatty acid, VFA; ammonia, NH₃) were measured by testing the inoculum and substrate (legumes vs. cereals). The inocula were different (p < 0.01) in OMd (818.2 vs. 799.4 g/kg OM for CI and FI respectively), A (255.0 vs. 267.1 ml/g OM), total VFA (67.3 vs. 53.2 mmol/g OM) and NH₃ content (21.2 vs. 19.8 mmol/l). Moreover, the significant differences in the (acetate + propionate)/butyrate ratio (5.02 vs. 4.09 for CI and FI respectively, p < 0.01) and in the branched chain proportion (isobutyrate + isovaleriate)/total VFA (0.044 vs. 0.031, p < 0.01) indicate that the inocula differed in fermenting legumes or cereals, but the equations for estimating caecal fermentation characteristics from those of faeces showed R² values from 0.673 to 0.975 (p ≤ 0.01). Our results confirm that in vitro fermentation characteristics of faeces were highly related to those of caecal content.     

纤维素酶对粗饲料人工瘤胃pH、氨态氮及产气量的影响

本试验分别以棉籽壳、苜蓿、小麦秸秆、玉米青贮、玉米秸秆为底物,采用人工瘤胃技术,研究不同水平纤维素酶对人工瘤胃pH、氨态氮浓度及产气量的影响。对照组未添加纤维素酶,试验1、2和3组分别添加纤维素酶140、280、420IU/mL。结果表明,不同水平纤维素酶的人工瘤胃pH无显著变化(P>0.05),氨态氮浓度变化不显著(P>0.05),但人工瘤胃最大产气量显著提高(P<0.05)。     

Gas and short‐chain fatty acid production from feeds commonly fed to red deer (Cervus elaphus L.) and incubated with rumen inoculum from red deer and sheep

Efficient red deer supplementary feeding depends on estimations of the nutritive value of offered feeds, frequently estimated with the use of equations derived from domestic ruminants. The aim of this study was to compare the 24‐hour in vitro true dry matter degradability (ivTD₂₄), in vitro gas production (GP) kinetic parameters, GP in 24 hr of incubation (GAS₂₄) and short‐chain fatty acid (SCFA) and microbial biomass (MBS) produced after 24‐hour incubation of feeds in inoculum prepared from sheep and red deer rumen fluid. Eleven feeds, frequently consumed by red deer in Slovenia, which occur either naturally (two fresh grasses, chestnut fruits and common and sessile oak acorns) or are fed as winter supplemental feeds (two grass hays, two grass silages, apple pomace, fresh sugar beetroot), were investigated. The in vitro GP kinetic parameters, GAS₂₄ and ivTD₂₄, did not differ between animal species. Amounts of SCFAs were greater (p < 0.05) when feeds were incubated in sheep inoculum, while molar proportions of acetic and propionic acids did not differ. Molar proportions of butyric acid produced during incubation of high fibre feeds did not differ between animal species, but were higher (p < 0.05) when feeds high in starch or sugar were incubated in red deer inoculum. Greater production of SCFA by sheep rumen microbes suggests better coverage of host animal with energy precursors, while greater production of MBS by red deer rumen microbes suggests better coverage of host animal with protein. Results also suggest that rumens of sheep and red deer are inhabited by different microbial communities, which did not affect the extent of in vitro GP and degradation of feeds used in the present experiment. However, the possibility exists that the divergent nutrient use could be a consequence of different priming by different feeds of the donor animal diets.     

Influence of Carotino oil on in vitro rumen fermentation,metabolism and apparent biohydrogenation of fatty acids

The study appraised the effects of Carotino oil on in vitro rumen fermentation, gas production, metabolism and apparent biohydrogenation of oleic, linoleic and linolenic acids. Carotino oil was added to a basal diet (50% concentrate and 50% oil palm frond) at the rate of 0, 2, 4, 6 and 8% dry matter of the diet. Rumen inoculum was obtained from three fistulated Boer bucks and incubated with 200 mg of each treatment for 24 h at 39°C. Gas production, fermentation kinetics, in vitro organic matter digestibility (IVOMD), volatile fatty acids (VFA), in vitro dry matter digestibility (IVDMD), metabolizable energy and free fatty acids were determined. Carotino oil did not affect (P > 0.05) gas production, metabolizable energy, pH, IVOMD, IVDMD, methane, total and individual VFAs. However, Carotino oil decreased (P < 0.05) the biohydrogenation of linoleic and linolenic acids but enhanced (P < 0.05) the biohydrogenation of oleic acid. After 24 h incubation, the concentrations of stearic, palmitic, pentadecanoic, myristic, myristoleic and lauric acids decreased (P < 0.05) while the concentration of linolenic, linoleic, oleic and transvaccenic acids and conjugated linoleic acid (CLAc9t11) increased (P < 0.05) with increasing levels of Carotino oil. Carotino oil seems to enhance the accumulation of beneficial unsaturated fatty acids without disrupting rumen fermentation.     

Using a novel macro in vitro technique to estimate differences in absorption rates of volatile fatty acids in the rumen

A novel macro in vitro system was used to test the theory that rumen proportions of acetate, propionate and butyrate are not representative of their respective net production rates. Whole rumen content (10–16 kg) from two cows was mixed with a bicarbonate buffer and incubated separately in two 40‐l in vitro vessels for 3 h. A total of six experimental periods were used. In this study, a total of six cows were used and fed 1/8 of the daily ration by hand every 3 h. To obtain differences in rumen volatile fatty acids (VFA) composition, 1 l of acetate (416 mm ), propionate (108 mm ), butyrate (79 mm ), lactic acid (300 mm ) or nothing was infused during 24 h into the rumen before collection of representative samples of rumen contents. Infusions of acids were then continued during the in vitro incubations in exact proportion to the digesta removed from the rumen. In Periods 1 and 2, the cows were alternatively infused with acetate or nothing. In Periods 3 and 4, the infusions consisted of propionate or butyrate and in Periods 5 and 6 of lactate or nothing. Nine liquid samples were obtained between 3 and 180 min after the start of incubation and analysed for concentrations of VFA. Changes in proportions of individual VFA were estimated by linear regression. No differences in VFA proportions were observed in the absence of infusion (p > 0.5) over time, but when individual VFA were infused, their respective proportions increased. This was interpreted as the result of a decreased in vitro fermentation rate of digesta substrates compared with that in the rumen. Lactate infusion increased butyrate proportion in vitro. It is concluded that this study could not provide any evidence that ruminal VFA proportions are unrepresentative of the proportions of net production.     

Effects of rare earth element lanthanum on rumen methane and volatile fatty acid production and microbial flora in vitro

The objectives of the trial were to study the effects of rare earth element (REE) lanthanum (La) on the in vitro rumen methane (CH₄) and volatile fatty acid (VFA) production and the microbial flora of feeds. Four feed mixtures with different levels of neutral detergent fibre (NDF), that is 20.0% (I), 31.0% (II), 41.9% (III) and 52.7% (IV), were formulated as substrates. Five levels of LaCl₃, that is 0, 0.4, 0.6, 0.8 and 1.0 mmol/kg dry matter (DM), were added to the feed mixtures, respectively, as experimental treatments in a two‐factor 5 × 4 randomized design. The in vitro incubation lasted for 24 h. The results showed that supplementing LaCl₃ increased the total gas (p < 0.001) production and tended to increase the total VFA production (p = 0.072) and decreased the CH₄ production (p = 0.001) and the ratios of acetate/propionate (p = 0.019) and CH₄/total VFA (p < 0.001). Interactions between LaCl₃ and NDF were significant in total gas production (p = 0.030) and tended to be significant in CH₄ production (p = 0.071). Supplementing LaCl₃ at the level of 0.8 mmol/g DM decreased the relative abundance of methanogens and protozoa in the total bacterial 16S rDNA analysed using the real‐time PCR (p < 0.0001), increased F. succinogenes (p = 0.0003) and decreased R. flavefaciens (p < 0.0001) whereas did not affect R. albus and anaerobic fungi (p > 0.05). It was concluded that LaCl₃ decreased the CH₄ production without negatively affecting feed digestion through manipulating rumen microbial flora when feed mixtures with different levels of NDF were used as substrates.     

体外产气量法研究日粮中添加不同水平棉籽油对绵羊瘤胃发酵动力学的影响

试验采用体外产气量法研究日粮中添加不同水平的棉籽油对绵羊瘤胃发酵功能的影响。棉籽油的添加水平分别设0(对照组)、1%、2%和3%。结果表明:日粮添加不同水平的棉籽油使人工瘤胃的最大产气量依次降低,但各处理组差异不显著(P>0.05)。与对照组相比,添加棉籽油并未显著改变发酵液pH值和NH3-N浓度。与对照组相比,添加棉籽油可以降低羧甲基纤维素酶(CMCase)和木聚糖酶(XYLase)活性,仅在发酵48h后,各处理组的CMCase活性达到显著水平(P<0.05),但各处理组差异不显著(P>0.05)。与对照组相比,随棉籽油添加水平的升高可以依次降低干物质(DM)和中性洗涤纤维(NDF)的降解率,发酵48h后,2%和3%组DM显著低于对照组(P<0.05),但两者间差异不显著(P>0.05)。与对照组相比,添加棉籽油并未显著影响总挥发酸浓度(TVFA)、乙酸摩尔百分比、丙酸摩尔百分比和乙丙酸比。